Does a mother taking two 1000 DZD banknotes from her son in exchange for giving him one 2000 DZD banknote, without immediate possession, constitute usury (riba)?

Currency exchange is called sarf, and it is subject to the following rulings: If the currencies are the same, equality and immediate possession (taqabud) at the time of the transaction are required. However, if the currencies are different, only immediate possession (taqabud) is required. Fiat currencies have the same rulings as gold and silver with regard to riba (usury/interest) and zakat. It is not permissible for the contracting parties to part ways until each has received the full amount of the exchange. It is permissible to appoint an agent for sarf, even if the agent handles both sides of the contract and takes possession from himself for his principal.